feat: localizable dialog title for enter section title

[anatawa12]

What

Fix #5665

ついでに小さなrefactorを入れました

変更量の小ささからCHANGELOGはなしでいいと判断してます。

Why

Additional info (optional)

Checklist

• Read the contribution guide
• Test working in a local environment
• (If needed) Add story of storybook
• (If needed) Update CHANGELOG.md
• (If possible) Add tests

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 18 lines in your changes missing coverage. Please review.

Project coverage is 20.24%. Comparing base (41936c1) to head (bfcaf76).
Report is 8 commits behind head on develop.

Files	Patch %	Lines
packages/frontend/src/pages/page-editor/common.ts	0.00%	14 Missing and 1 partial ⚠️
...c/pages/page-editor/els/page-editor.el.section.vue	0.00%	2 Missing ⚠️
...ges/frontend/src/pages/page-editor/page-editor.vue	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #14401       +/-   ##
============================================
- Coverage    39.91%   20.24%   -19.67%     
============================================
  Files         1545      724      -821     
  Lines       190505   100288    -90217     
  Branches      2654     1050     -1604     
============================================
- Hits         76046    20308    -55738     
+ Misses      113898    79438    -34460     
+ Partials       561      542       -19     

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[syuilo]

🙏🏿